Explanation of the internal structure of industrial robots

The pace of development of China's manufacturing industry is getting faster faster, the number of industrial robots used in Chinese factories is increasing. If you want to become an industrial robot technical talent, you must understand the internal structure of industrial robots. The following will introduce the structure of general industrial robots.

1. Robot drive device

Concept: To make the robot run, a transmission device must be installed for each joint, that is, each degree of freedom of movement. Function: Provide the motive force for the movement of each part joint of the robot.

Drive system: It can be hydraulic drive, pneumatic drive, electric drive, a comprehensive system that combines them; it can be directly driven indirectly driven through mechanical transmission mechanisms such as synchronous belts, chains, gear trains, harmonic gears, etc.

1. Electric drive device

Electric drive devices have simple energy, wide speed range, high efficiency, high speed position accuracy. However, they are often connected to a reduction gear, making direct drive difficult.

Electric drive devices can be divided into direct current (DC), alternating current (AC) servo motor drives stepper motor drives. The brushes of DC servo motors are easy to wear spark. Brushless DC motors are also increasingly widely used. Stepper motor drives are mostly open-loop control, which is simple to control but very powerful, are mostly used in low-precision, low-power robot systems.

Before the electric motor is powered on, the following checks must be performed:

1) Is the power supply voltage appropriate (overvoltage may cause damage to the drive module); The +/- polarity of the DC input must be connected incorrectly, the motor model current setting value on the drive controller is appropriate ( too large at the beginning);

2) The control signal line should be connected securely. It is best to consider shielding issues at industrial sites (such as using twisted pair cables);

3) Don't connect all the necessary wires at the beginning. Just connect the most basic system. Once it is running well, you can connect them step by step.

4) Make sure to understand the grounding method, choose floating method.

5) Within half an hour of starting operation, closely observe the status of the motor, such as whether the movement is normal, the sound temperature rise. If any problems are found, stop the machine immediately adjust it.

2. Hydraulic drive

This is accomplished through a high-precision cylinder piston, linear motion is achieved through the relative movement of the cylinder piston rod.

Advantages: high power, can omit the reduction device directly connect to the driven rod, compact structure, good rigidity, fast response, servo drive has high precision.

Disadvantages: It requires an additional hydraulic source, which is prone to liquid leakage is suitable for high low temperature environments. Therefore, hydraulic drive is currently mostly used in ultra-high power robot systems.

Choose the right hydraulic oil. Prevent solid impurities mixing into the hydraulic system, prevent air water invading the hydraulic system. Mechanical operation should be gentle smooth. Mechanical operation should avoid roughness, otherwise it will inevitably produce impact loads, causing frequent mechanical failures greatly shortening the service life. Pay attention to cavitation overflow noise. During operation, always pay attention to the sound of the hydraulic pump the overflow valve. If the hydraulic pump has "cavitation" noise it cannot be eliminated after exhaust, the cause should be found out the fault should be eliminated before use. Maintain a suitable oil temperature. The operating temperature of the hydraulic system is generally controlled between 30 80°C.

3. Air pressure drive

The pneumatic drive has a simple structure, is clean, has sensitive movements, has a buffering effect. However, compared with the hydraulic drive, it has lower power, poor rigidity, high noise, difficult speed control, so it is mostly used for point control robots with low precision.

(1) It has the characteristics of high speed, simple system structure, easy maintenance low price. It is suitable for use in robots with medium small loads. However, due to the difficulty in achieving servo control, it is mostly used in program-controlled robots, such as loading unloading stamping robots.

(2) In most cases, it is used to implement two-position limited-point control in medium small robots.

(3) Currently, most control devices use programmable controllers (PLC controllers). In flammable explosive environments, pneumatic logic elements can be used to form control devices.

2. Linear transmission mechanism

The transmission device is the key part connecting the power source the moving connecting rod. According to the joint form, the commonly used transmission mechanism forms include linear transmission rotary transmission mechanism.

The linear transmission method can be used for the X, Y, Z-axis drive of rectangular coordinate robots, the radial drive vertical lifting drive of cylindrical coordinate structures, the radial telescopic drive of spherical coordinate structures.

Linear motion can be converted into linear motion by transmission elements such as gear racks, lead screws nuts. It can also be driven by a linear drive motor directly generated by the piston of a cylinder hydraulic cylinder.

1. Gear rack device

Usually the rack is fixed. The rotational motion of the gear is converted into linear motion of the pallet.

Advantages: simple structure.

Disadvantages: large hysteresis.

2. Ball screw

The balls are embedded in the spiral grooves of the screw nut, the balls can circulate continuously through the guide grooves in the nut.

Advantages: small friction, high transmission efficiency, no creep, high precision

Disadvantages: high manufacturing cost complex structure.

Self-locking problem: In theory, ball screw pairs can also be self-locking, but this self-locking is used in practical applications. The main reasons are: poor reliability high processing costs; because the diameter-to-lead ratio is very large, a self-locking device such as a worm gear is generally added.

3. Rotary transmission mechanism

The purpose of using a rotary transmission mechanism is to convert the higher speed output by the motor drive source into a lower speed obtain a larger torque. The rotary transmission mechanisms that are widely used in robots include gear chains, synchronous belts, harmonic gears.

1. Gear chain

(1) Speed relationship

(2) Torque relationship

2. Synchronous belt

The synchronous belt is a belt with many teeth, which meshes with a synchronous pulley with teeth. It is equivalent to a soft gear when working.

Advantages: no sliding, good flexibility, low price, high repeatability.

Disadvantages: Has certain elastic deformation.

3. Harmonic gear

The harmonic gear is composed of three main parts: a rigid gear, a harmonic generator a flexible gear. Generally, the rigid gear is fixed the harmonic generator drives the flexible gear to rotate. 

main feature:

(1) The transmission ratio is large, with a single stage ratio of 50-300.

(2) Smooth transmission high load-bearing capacity.

(3) High transmission efficiency, up to 70% - 90%.

(4) High transmission accuracy, 3-4 times higher than ordinary gear transmission.

(5) The hysteresis is small can be less than 3'.

(6) Intermediate output cannot be obtained the flexspline stiffness is low.

Harmonic drive devices have been widely used in countries with advanced robot technology. In Japan alone, 60% of robot drive devices use harmonic drive.

The robot sent to the moon by the United States uses harmonic transmission devices in all its joints, one of its upper arms uses 30 harmonic transmission mechanisms.

The mobile robot "Moon Lander" sent to the moon by the former Soviet Union had eight wheels installed in pairs, all of which were driven individually by a closed harmonic drive mechanism. The ROHREN GEROT R30 robots developed by Volkswagen in Germany the VERTICAL 80 robot developed by Renault in France all use harmonic drive mechanisms.

4. Robotic Sensing System

1. The perception system consists of internal sensor modules external sensor modules to obtain meaningful information about the internal external environmental states.

2. The use of intelligent sensors improves the robot's mobility, adaptability intelligence.

3. The use of intelligent sensors improves the robot's mobility, adaptability intelligence.

4. For some special information, sensors are more effective than human perception systems.

5. Robot position detection

Rotary optical encoders are the most commonly used position feedback devices. Photodetectors convert light pulses into binary waveforms. The angle of rotation of the shaft is obtained by counting the pulses, the direction of rotation is determined by the relative phase of the two square wave signals.

Inductosyn outputs two analog signals - the sine cosine of the shaft angle. The shaft angle is calculated the relative amplitudes of the two signals. Inductosyn is generally more reliable than encoders, but has lower resolution.

The potentiometer is the most direct form of position detection. It is connected in a bridge can generate a voltage signal proportional to the shaft angle. However, it has low resolution, poor linearity is sensitive to noise.

A tachometer outputs an analog signal that is proportional to the shaft's rotational speed. If there is no such speed sensor, a speed feedback signal can be obtained by differentiating the detected position with respect to time.

6. Robot force detection

Force sensors are usually installed in the following three locations on the manipulator arm:

1. Installed on the joint driver. It can measure the torque force output of the driver/reducer itself. But it cannot detect the contact force between the end effector the environment well.

2. Installed between the end effector the terminal joint of the manipulator, it can be called a wrist force sensor. Usually, three to six force/torque components applied to the end effector can be measured.

3. Installed on the "fingertips" of the end effector. Usually, these force-feeling fingers have built-in strain gauges that can measure one to four components of force acting on the fingertips.

7. Robot-Environment Interaction System

1. The robot-environment interaction system is a system that realizes the mutual connection coordination between industrial robots equipment in the external environment.

2. Industrial robots external equipment are integrated into a functional unit, such as a processing manufacturing unit, welding unit, assembly unit, etc. It can also be the integration of multiple robots, multiple machine tools equipment, multiple parts storage devices, etc.

3. It can also be that multiple robots, multiple machine tools equipment, multiple parts storage devices, etc. are integrated into a functional unit to perform complex tasks.

8. Human-computer interaction system

The human-machine interaction system is a device that enables the operator to participate in the robot control communicate with the robot. The system can be summarized into two categories: instruction giving device information display device.